The usual method of joining sections of pipe made of a thermoplastic material is to provide one end of such a section of plastic pipe with an integral bell portion. This bell portion is formed by heating the end section and distorting the end section over a mandrel to form the properly sized and enlarged bell. Most desirably, an inwardly opening annular groove is provided during or subsequent to this belling operation so that a sealing ring of an elastomeric material may be incorporated either removably or fixedly in the bell portion. This sealing ring is sized to sealingly engage the spigot end of another section of such plastic pipe, thus forming a fluid-tight joint between these two sections. However, should these plastic pipe sections incorporate certain strengthening features on the outer surface thereof, specifically helical, the formation of such a watertight bell and spigot joint becomes more difficult. The spigot end of such a pipe no longer presents a smooth, uninterrupted outer circumference to which such a bell supported sealing ring can sealingly engage.
Accordingly, in the past it has been found necessary to alter the outer surface of the ribbed spigot in order to provide such a sealing surface. In one known joint construction, an annular groove is cut completely through the intersecting ribs at the spigot end of a ribbed pipe. A conventional sealing gasket is positioned in the groove and forms a seal between the resulting smooth annular surface and the inner surface of a surrounding pipe bell. Another system is disclosed in U.S. Pat. No. 3,635,505 in which a sealing ring is incorporated on the spigot portion between adjacent projecting rib portions. A groove is machined between intervening projecting ribs so as to connect the thus rib defined groove and form a seat for a specially formed sealing ring, which includes a straight section which corresponds to the machined interconnecting slot. A system which uses a more conventional sealing ring, however, would be more desirable.
It is also known to adhere a rubber sealing ring in a groove in the bell portion of a pipe joint.